It could be a bad ground, your interlock system, the starter, corrosion... The list goes on. Time to break out the Volt meter!
First thing I would check is a proper ground wire and that the starter is getting voltage when you turn the key. If after several attempt it does start that removes any locking up issues. If the wires are clean and good contact i would next check the starter switch. making sure it's sending voltage to the starting system when you turn the key. This could be you troubled area. Electrical issues are nasty, intermediate electrical issue are even worse. As for the sputtering, first things first- Lets get you running.